A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Certain devices within the network, such as routers, maintain tables of information that describe routes through the network. A “route” can generally be defined as a path between two locations on the network. Upon receiving an incoming data packet, the router examines destination information within the packet to identify the destination for the packet. Based on the destination, the router forwards the packet in accordance with the routing table.
The physical connection between devices within the network is generally referred to as a link. A router uses interface cards (IFCs) for receiving and sending data packets via network links. These IFCs are installed in ports known as interfaces and are configured using interface configurations.
Generally, a router maintains state information. For example, a router may maintain state information representing the current state of the interfaces between the router and the network. Such state information may include information representing the state of one or more IFCs, such as the current configuration of the IFCs. As additional examples, a router may maintain state information representing the state of one or more packet forwarding engines (PFEs), one or more routing engines, or other resources within the router.
In particular, a process, e.g., a control node known as a “routing engine,” operating within a router may maintain the state information and communicate changes to the state information to various other processes or components within the router. These other processes or components are sometimes referred to as “consumers,” because they receive and utilize the state information maintained by the operating system. These consumers make use of the state information when performing their various functions.
As the complexity of conventional networks has increased in recent years, management of the state information within a router or other network device has likewise become a significant challenge. Some existing methods for managing state information involve caching the information within the operating system, and issuing state change notification messages to software modules executing within the router. In response, the software modules retrieve the state information from the operating system.
To increase reliability, some routers may include a primary routing engine and one or more standby routing engines. Both primary and standby routing engines may require state information. In the event that the primary routing engine fails, one of the standby routing engines assumes control of the routing resources to continue operation of the router. The process of switching control of routing functions between the primary and standby routing engines is often referred to as failover. In some instances, to assume proper control and ensure operation, the standby routing engine is forced to “relearn” the lost state information from each resource, e.g., by power cycling the router resources to a known state. This causes an interruption in packet forwarding while the router resources restart operations.
Routers have not only developed to be more reliable, but also to meet increasing bandwidth demands. One way to meet increasing bandwidth needs is to use multi-chassis routers, i.e., routers in which multiple routing devices are physically coupled and configured to operate as a single router. For example, a multi-chassis router may contain multiple line card chassis (LCCs), which include one or more IFCs, and a central switch card chassis (SCC), which forward packets between the LCCs and provides top-down management of the multi-chassis router. Because multi-chassis routers combine resources of multiple routing devices, multi-chassis routers typically have much higher bandwidth capabilities than standalone routers. The use of multi-chassis routers can simplify and improve routing on a service provider network by consolidating routing functions onto fewer routers. However, forwarding state information to each consumer in a multi-chassis router can be significantly more difficult than in a standalone router.